wp_register_script function include my own created javascript file from plugin directory and also include jquery file.
$local_variables contains array in which you have to pass all variables with key which you want to access into your fb.js file.
wp_localize_script function will pass this array into js file & you can access theses variables in javascript file like vars.app_id and vars.name !!

Like this:

Some OOP concepts

The main difference between OOP and functional programming is that the data and code are bundled together into one entity, which is known as an object.

During the execution of an object’s method, a special variable called $this is automatically defined, which denotes a reference to the object itself.

if a parent class declares a member as public, the inheriting child class must also declare it as public. Otherwise, the child would not have an is-a relationship with the parent, which means that anything you can do with the parent can also be done with the child.

When no access modifier is given for a method, public is used as the default.

You can define any number of methods as abstract, but once at least one method of a class is defined as abstract, the entire class needs to be declared as abstract, too.

In PHP, a method is either abstract (without code) or it’s fully defined.

PHP chose interfaces as an alternative to multiple inheritance.

An interface is declared similar to a class but only includes function prototypes (without implementation) and constants.

Note: Interfaces are always considered to be public; therefore, you can’t specify access modifiers for the method prototypes in the interface’s declaration.

There are times where you might want to make sure that a method cannot be re-implemented in its derived classes. For this purpose, PHP supports the final access modifier for methods that declares the method as the final version, which can’t be overridden.